Sold as a single piston and although for Turbos is from original Rover casting and tooling to run on 5psi turbo boost. Now with 9.38cc. They use our mega ringset
C-AJJ3379-40.
If using more boost you need to be working on a lower CR with a total cylinder volume of 55cc in piston/block/head gasket and cylinder head.
Also when increasing boost pressures it is essential to have a modified ignition advance/retard curve to prevent detonation and ensure the inlet charge temperature does not exceed 40 degrees C by the fitment of a suitable intercooler.
If our advice is not followed it is very likley you will break the ring lands on your new pistons.